What is the purpose of non-coding DNA?
We put this to Julian Huppert, Member of Parliament for Cambridge and lapsed academic, formerly working on genomics....
Julian - Well, there are various ways of thinking about it and we’re still trying to understand some of it. In some ways, the coding sections are the recipes for the proteins that we have. The genes and the non-coding DNA are very important in saying how much of this should be there, when is it turned on, when is it turned off. All of those controls are hidden in the non-coding sections of DNA. There are some other bits which are old things which we don't really use such as genes which were useful a few million years ago, we still have bits lying around. Also there are some bits which really are junk. They are viruses that have crept into our genome over time.
What I used to work on was something called the G-quadruplex. DNA of the right sequence can form four stranded knots. These can act as off-switches which stop the gene from being active. It started off as an interesting theoretical curiosity. We actually found that almost half of all human genes seem to have these switches in a way that could be playing a role in turning them on and off. In particular, most cancer genes had these little structures which form little knots at the beginning of the gene, marking it as off.
Diana - So-called junk DNA can be acting in other ways as on/off switches, packaging for coding DNA or instructions on how that DNA is unpacked. Imat faal said on the forum that DNA can have another use altogether, finger printing for identification.
Well a few years ago it was found that the "junk dna" that was used (and stored/compared) for ID purposes under UK law included enough information to discern certain diseases and illness proclivities. (I will dig out a reference)
The UK National DNA database stores DNA from people across the whole of the UK - not just England and Wales. And whilst the criteria for harvesting/accessing/storing does vary from Scotland - the information stored once the initial sample is destroyed is the same across both Jurisdictions. The whole thing would be seen as a complete transgression of civil liberties under US Law (both state or federal) and tends to be under EU law (national, supranational or ECHR). It's complicated...
Am I right in saying that recently, junk DNA is a target for cleavage by Protein complex's to create secondary miRNA which then go on to regulate gene expression, eg AGO targets a sequence to cleave, creates miRNA that initiate viral response? James the novice, Tue, 21st Jun 2011